1. Field of the Invention
This invention relates to a gas sensor, and more particularly to a gas sensor which detects a gas by utilizing a phenomenon that a solid compound is reduced, in the presence of a small amount of hydrogen gas or hydrogen containing compound gases, by a reducing activity of hydrogen atoms dissociated and adsorbed by a catalytic metal disposed in the vicinity of the solid compound.
2. Description of Prior Art
Conventional gas sensors are generally of a contact burning type or of a semiconductor type. In a gas sensor of the contact burning type, a catalytic metal such as platinum or palladium is heated by a heater so as to cause a gas to be burned when the gas comes into contact with the metal and a change in dielectric constant caused by burning of the gas is electrically detected. In a gas sensor of the semiconductor type, the gas sensor is used in the heated state for a reason of a gas selection characteristic, response characteristic, characteristic of the device, etc. and a change in electrical characteristics caused by adsorption of the gas is detected.
However, these conventional gas sensors involve a problem of explosion because heating or burning is effected for detecting a combustible or explosive gas. Thus, the conventional gas sensors have problems in safety. Furthermore, the gas sensor of conventional type is rather poor in detection accuracy because its detected signal is electrical, thus it is a risk influence to the electric circuit which conducts the said detected signal by electromagnetic induction, for example jamming in radio wave or electrical noises.
In addition, since the device is heated, the deterioration of the device is accelerated and the characteristics of the device are bound to become unstable, which renders the reliability of the gas sensor to be lowered.